Ground storage unit with centersupported roof



March 22, 1966 c. o. HUNTRESS ET AL 3,241,707

GROUND STORAGE UNIT WITH CENTER-SUPPORTED ROOF Filed Jan. 20, 1964 2 Sheets-Sheet 1 FIG. 2.

6 llb INVENTORS Russell C. Proctor Charles 0. Hunfress ATTORNEY March 22, 1966 c. o. HUNTRESS ETAL GROUND STORAGE UNIT WITH CENTER-SUPPORTED ROOF Filed Jan. 20, 1964 2 Sheets-Sheet 2 NMNXD WWM.

m m \l 0 N 1 m ussell C. Proctor Charles OvHumress ATTORNEY United States Patent 3,241,707 GROUND STORAGE UNIT WITH CENTER- SUPPGRTED ROOF Charles 0. Huntress and Russell C. Proctor, Leawood,

Kans., assignors to Conch International Methane Limited, Nassau, Bahamas, a company of Bahamas Filed Jan. 20, 1964, Ser. No. 338,781 6 (Ilaims. (Cl. 220-18) This invention relates to large storage tanks for cryogenic liquids. While intended primarily for LNG (liquefied natural gas), the principle could be applied to other liquids which have a temperature at atmospheric pressure below the freezing point of water saturated soils. The storage of large quantities of such liquids has presented a diflicult problem, both economic and technical. Natural gas is today stored in the gaseous phase in its original natural reservoirs, in depleted oil and gas reservoirs, aquifer storage installations and in high pressure tankage at low Z factor. As a cryogenic liquid LNG at its equilibrium temperature (259 F.) at atmospheric pressure is stored in above ground double-walled insulated tanks similar to those used for liquid oxygen, or liquid nitrogen. It is also stored in in-ground pits utilizing the impervious nature of water saturated frozen earth with a metallic cover or roof over the pit area for the collection of the boiloff vapors. The hole is in this case generally made as compact as possible to minimize surface loss of temperature, and this requires the hole to be very deep for a large reservoir-typically over 150 feet in depth, which is expensive to construct.

In particular, the recent interest in large-scale use of LNG for the peak shaving in gas distribution systems has centered attention on the problem of economically and safely storing large quantities of LNG. The storage method presented here essentially consists of a shallow tank erected in an areas with a high water table but where the excavation could be made using the conventional methods of excavation and pumping from sumps with or without reliance upon sheet piling or well pointing. The walls of the storage tank are of a design which could utilize prestressed concrete or similar material with a vapor-tight liner which may be made of plastic, metal or other impervious material and can withstand low temperatures and remain vapor and liquid tight. The tank has only an earth or rock bottom with insulation on the bottom held in place by an amount of earth or other material of density sufiicient to keep the insulation from floating up in the stored liquid.

It is a major object of the present invention to provide a large-scale in-ground or partially in-ground reservoir for LNG and similar liquids, which will reduce the capital cost of the storage and yet provide all of the safety advantages inherent to in-ground storage. This reservoir can be constructed in a wider range of locations than storage completed in areas more dependent upon the physical properties of the frozen earth at storage temperatures; does not require expensive prefreezing of the ground, and does not require deep and expensive excavation, and because of its shall-ow depth eliminates or reduces many of the water control problems associated with deeper installations.

The specific nature of our invention as well as other objects and advantages thereof will clearly appear from a description of a preferred embodiment as shown in the accompanying drawings, in which:

FIG. 1 is a sectional elevation of the entire tank and adjacent terrain;

FIG. 2 is a sectional view taken on line 2-2 of FIG. 1 of the central portion of the roof structure;

FIG. 3 is an enlarged transverse sectional view of a 3,241,707 Patented Mar. 22, 1966 portion of the wall structure, showing the manner in which it supports the roof; and

FIG. 4 is a sectional view showing typical details of the supporting post structure; and FIG. 4a is a view of an alternative roller support for the roof beams.

While it is true that the tank has a larger exposed area for heat leak than the compact tank having a diameter in depth ratio approaching 1:1, most of the exposed area is horizontalnamely, floor and roof, and therefore can be less expensively insulated. Insulation on both the floor and roof is essentially held in place by its own weight.

As best seen in FIG. 1, the storage tank or reservoir is relatively shallow and of large diameter; typical dimensions of such an installation would include a storage unit having a Wall height of 60 feet from roof line to floor and 270 feet in diameter. The ground can be largely excavated by scrapers or draglines and in general, by using the same techniques employed in excavating for the foundations of large buildings, since the depth of the excavation below grade will be in the order of one-half the depth of the tank. It is desirable for the present present purpose to extend the excavation below the water table, a standard technique for keeping seepage water out of the excavation during digging can be employed, as by sheet piling and well-pointing, to enable excavation in the dry.

Piling is shown under the wall footers and this feature may or may not be required if the soil bearing is adequate for the support of the wall and its portion of the roof load. The piling need not be of permanent materials because once the tank is put in service by filling with the extremely cold liquid, the ground for several feet around the tank becomes solidly frozen eliminating the dependence on the piling.

The shallow tank is necessarily of large diameter, and therefore requires a large roof span; if unsupported, such a large roof span would be very expensive. However, according to the invention, the center of the roof span is supported by one or more piles or posts extending upward directly from the floor of the tank. This is feasible due to the relatively short distance (e.g., sixty 'feet), which permits available steel piping to be used, and this same piping can also be used as conduit for filling and emptying the tank, containing depth gauge, pumps, etc., thus effecting a further economy.

After the excavation is dug to a sufficient depth, a system of central supporting piles 8 is erected at the center of the exavation extending upwardly to the height of the center of the roof 9 of the tank, the center being considered as a small area of the roof which approximates the geometric center point of the roof, which is negligibly small in comparison with the total roof area. For the typical dimensions given, namely a 270-foot span, center support is adequate with appropriately-sized supporting members. As shown, four piles 11 are used, appropriately trussed, as by steel members 12, which may be channel sections, and a circular supporting ring 13 at the top for end support of girders 14, (which may be I-beams, plate girders or other structural members) which in turn support intermediate members such as purlins 16, all being suitably fastened together as by welding or riveting to form a rigid structure of the necessary strength. If low temperature liquids such as LNG are to be stored, this structure should be of a material suitable for low temperature application such as aluminum or nickel steel.

After the soil bottom of the tank has been shaped or formed, the floor insulation 6 is placed. This insulation is preferably of a type such as Foamglas or other cellular insulation whose thermal conductivity is only slightly affected by wetting with water or LNG and need not be kept dry in order to preserve its thermal insulating qualities. Since this type of insulation is bouyant and will tend to fioat when the tank is filled or if water seeps into the tank before filling, a layer of dirt, gravel, or any other material of suitable density '7, is placed over the insulation 6 to prevent it from floating.

The wall footers 31, preferably of prestressed concrete, are constructed and moved to their position indicated in the drawing and placed as indicated on a ring of previously driven piles 32 if required or otherwise on a non-heaving bedding material such as graded sand. The prestressed wall panels 2 are erected on the footers 31 with their cast-in-place liner sheets. The panel liners are seal welded one to the next, the panels are intergrouted, the prestressing is applied and the exterior grout protection applied in accordance with known practice. Outside this, wall insulation is applied and partial backfill completed to the level that insulation 26 is placed and then the remainder of the backfill completed. Insulation 26 is a horizontal layer of water-impervious insulation such as Foamglas provided below the grade line out to a distance of 20 or 30 feet from the wall 2, and tapering in thickness some eight inches at the wall 2, to some four inches at its perimeter. This serves to insulate the frozen ground around the perimeter of the tank from the relatively warm surface and thus aids in retaining the fluid-sealing properties of the tank by maintaining the frozen condition of the ground at the base of the tank.

Dikes will only be necessary to contain the design volume of the inventory in the tank above the minimum water table in event of spillage. If the entire storage can be constructed below grade such that the maximum design liquid level is sufliciently below the minimum water table, then no dikes are required.

The roof is completed by placing sheet 17 on the sup porting framework 14, 16. The roof sheet materials are subject to the same temperature design specifications as the supporting framework. At the perimeter, the roof sheet is brought down as shown at 18 into sealing relation with the wall 2 and provided with suitable contraction and expansion-accommodating means, as indicated at 19. The ends of beams 13 are similarly supported on walls 2 in such a manner as to permit thermal contraction and expansion, as indicated schematically by bolt 22 passing through slot 21 in the lower flange of beam 14. Alternatively, suitable rollers 20 may be employed, as shown in FIG. 411, although any suitable means for this purpose can be employed. Suitable insulation must be provided on the roof, which insulation is shown at 23 as a layer of, e.g. Foamglas or other suitable insulation, typically six to eight inches thick. This insulation is covered with several plies of built-up roofing 24, and preferably finished with a light-reflecting surface 34 on top to minimize solar heating and transmission of heat in general.

The posts 11 are hollow steel conduits and one or more of them will be used for filling and emptying the tank. A filling line is shown at 27. The same post (or another post) may be suitably apertured near the top as shown at 28 and used with a suitably-valved vent line 29 for venting off excess vapor pressure. Suitable apertures for filling and venting are shown at 31 and 32. Similarly a level gauge and any other auxiliary equipment may be housed in the posts, which thus serve multiple functions of support and operation.

It will be apparent that the embodiments shown are only exemplary and that various modifications can be made in construction and arrangement within the scope of our invention as defined in the appended claims.

We claim:

1. A ground storage tank or reservoir for large-scale storage of low-temperature fluid which is maintained at a temperature far below the freezing point of water,

(a) the minimum horizontal dimension of said tank being in the order of more than four times the magnitude of the greatest vertical dimension,

(b) said tank having a generally horizontal roof and a generally horizontal bottom,

(0) said tank comprising a relatively shallow excavation in the ground extending below the ground water table,

((1) an impervious, vertical, continuous load-bearing wall structure lining said excavation and extending vertically above the ground level to form the side walls of the tank,

(e) the bottom of the tank being formed by the bottom of said excavation,

(f) means supporting said roof at its outer perimeter upon said wall structure,

(g) vertical supporting means extending upwardly from the bottom of said tank, substantially at the center thereof, to the roof for supporting the roof at a very small area in comparison with the total area of the roof, said roof being supported entirely at its perimeter and at its center.

2. The invention according to claim 1, said vertical supporting means comprising at least one hollow pillar, and means for conducting fluid to and from said tank through said hollow pillar.

3. The invention according to claim 1, said vertical supporting means comprising several hollow pillars mechanically trussed together by intermediate structural members at a number of points along their length to form a single structural unit, and tank service equipment housed in said pillars.

4. The invention according to claim 1, and thermal insulation protecting all the surfaces of said tank from excessive thermal transmission, the thermal insulation of the floor of the tank being held in place by gravity.

5. The invention according to claim 4, said floor insulation being fioatable in the liquid of the tank, and weighting means on the upper surface of said insulation sufficient to keep said insulation in place.

6. The invention according to claim 4, the thermal insulation of the roof of the tank also being held in place by gravity.

References Cited by the Examiner UNITED STATES PATENTS 1,360,170 11/1920 Allinson 22045 2,531,742 11/1950 Pomykala 220-1 FOREIGN PATENTS 1,298,205 5/1962 France.

THERON E. CONDON, Primary Examiner.

GEORGE E. LOWRANCE, Examiner. 

1. A GROUND STORAGE TANK OR RESERVOIR FOR LARGE-SCALE STORAGE OF LOW-TEMPERATURE FLUID WHICH IS MAINTAINED AT A TEMPERATURE FAR BELOW THE FREEZING POINT OF WATER, (A) THE MINIMUM HORIZONTAL DIMENSION OF SAID TANK BEING IN THE ORDER OF MORE THAN FOUR TIMES THE MAGNITUDE OF THE GREATEST VERTICAL DIMENSION, (B) SAID TANK HAVING A GENERALLY HORIZONTAL ROOF AND A GENERALLY HORIZONTAL BOTTOM, (C) SAID TANK COMPRISING A RELATIVELY SHALLOW EXCAVATION IN THE GROUND EXTENDING BELOW THE GROUND WATER TABLE, (D) AN IMPERVIOUS, VERTICAL, CONTINUOUS LOAD-BEARING WALL STRUCTURE LINING SAID EXCAVATION AND EXTENDING VERTICALLY ABOVE THE GROUND LEVEL TO FORM THE SIDE WALLS OF THE TANK, (E) THE BOTTOM OF THE TANK BEING FORMED BY THE BOTTOM OF SAID EXCAVATION, (F) MEANS SUPPORTING SAID ROOF AT ITS OUTER PERIMETER UPON SAID WALL STRUCTURE, (G) VERTICAL SUPPORTING MEANS EXTENDING UPWARDLY FROM THE BOTTOM OF SAID TANK, SUBSTANTIALLY THE ROOF CENTER THEREOF, TO THE ROOF FOR SUPPORTING THE ROOF AT A VERY SMALL AREA IN COMPARISON WITH THE TOTAL AREA OF THE ROOF, SAID ROOF BEING SUPPORTED ENTIRELY AT ITS PERIMETER AND AT ITS CENTER. 